When creating a fluent api, how do they chained methods get context from previous methods?

Question

I'm looking at this open source project, and the fluent api looks like:

baseEngine.For<Foo1>()
            .Setup(f => f.Value)
              .MustEqual(1);

Then MustEqual method's parameter list it:

 public static M MustEqual<M, T, R>(this IMustPassRule<M, T, R> mpr, R value)
 {
    return mpr.MustPassRule(new EqualRule<R>(value));
 }

for more details: http://rulesengine.codeplex.com/SourceControl/changeset/view/9077#137411

So what I'm trying to get at is, the call to MustEqual is being passed only a single arguement, since it is fluent, is it somehow implicitly picking up other required parameters from the previously chained calls?

Are you talking about "this IMustPassRule<M, T, R> mpr"? If so then this is a C# construct to create an extension method for the IMustPassRule interface — Waleed Al-Balooshi
– Waleed Al-Balooshi, Commented Oct 18, 2011 at 16:18

Jesse C. Slicer · Accepted Answer · 2011-10-18 16:16:42Z

2

The state gets stored in the object itself by those previous methods, if necessary.

answered Oct 18, 2011 at 16:16

Jesse C. Slicer

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dtb · Accepted Answer · 2011-10-18 16:16:48Z

0

You are looking at an Extension Method.

Extension Methods allow static methods to be invoked with instance method syntax. For instance,

something.MustEqual(1);

is equivalent to

RulesHelper.MustEqual(something, 1);

answered Oct 18, 2011 at 16:16

dtb

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Emond · Accepted Answer · 2011-10-18 17:10:11Z

0

A nice example can be found in LINQ

The IEnumerable<T>.OrderBy returns an IOrderedEnumerable<T>

This second interface keeps track of the order so the IOrderedEnumerable<T>.ThenBy is able to do a sub-sort. To make things smooth the interface derives from IEnumerable<T>

edited Oct 18, 2011 at 17:10

answered Oct 18, 2011 at 16:24

Emond

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